Liquid-applied waterproofing membranes are known. In roofing applications they are used as an alternative to prefabricated sheet membranes, offering easier application especially in the case of complex roof geometries and for refurbishment tasks, providing a flexible seamless roof coating which is fully adhered to the substrate.
Liquid-applied waterproofing membranes on roofs have to fulfill demanding requirements. They need to have a low viscosity to be applied as self-levelling coatings and a sufficiently long open time to enable hand application, but still cure fast in order to quickly lose their vulnerability. When fully cured the roofing membrane needs to have durable elasticity and strength in order to protect the building effectively from water ingress in a broad temperature range and under outdoor weathering conditions, such as wind forces, ponding water, frost, strong sunlight irradiation, microbial attack and root penetration.
State-of-the-art liquid-applied waterproofing membranes are often reactive polyurethane compositions, formulated as one-part or as two-part systems, also called single-component or two-component systems, respectively. Two-part systems are more complex to apply, requiring special mixing equipment and proper metering of the two components, since mistakes in mixing quality and/or stoichiometry strongly affect the membrane performance. One-part systems are easy to apply, but prone to curing defects. State-of-the-art one-part systems comprise blocked amine hardeners, in particular oxazolidines, to prevent excessive gassing from carbon dioxide formation on curing. They generally contain considerable amounts of solvents to guarantee low viscosity and sufficient shelf life. Attempts spurred by tightening VOC regulation to reduce the solvent content of such one-part systems typically result in difficulties with shelf life stability and bad workability because of high viscosity, as the viscosity of the compositions starts on a higher level and increases further from premature crosslinking reactions between the NCO groups of the prepolymer and the oxazolidine hardeners during storage. Further drawbacks of conventional one-part membranes are related to slow curing and unpleasant odours caused by the emission of the blocking agent, a volatile aldehyde or ketone.
WO 2009/010522 and WO 2008/000831 disclose compositions containing polyaldimines as blocked amine hardeners, which are usable i.a. as one-component elastic coatings, preferably for flooring purposes.
U.S. Pat. No. 5,087,661 discloses compositions comprising polyaldimines, i.a. a long-chain polyether aldimine derived from a polyethertriamine and benzaldehyde, which are usable as water proof material, flooring material, sealing material, wall covering material and paint.
There is a strong need for high quality liquid-applied waterproofing membranes with low viscosity in order to be able to formulate products with very low or no solvent content.